You will probably get a better answer if you send this question to
us...@subversion.apache.org, since it concerns server configuration and not the TortoiseSVN client itself.
Anyway I tried it out and I believe the * = r is granting read access (and the remaining rules are not checked). However specialuser should not be able to commit to anything other than /directory/subdirectory, when I tried it I got the expected error message Access to '/directory' forbidden.
Kind regards,
Daniel